Drilling tools for machine tool and method of producing the same

ABSTRACT

The invention concerns a drilling tool for machine tools. The drilling tool comprises a drill body with two chip-conveying grooves which are delimited at their flanks by helically curved ribs. Disposed at the end of the drill body is a drill head which comprises two segment parts, which are separated from each other by opposite axially aligned chip spaces, and two cutting plates which are each disposed in a recess in the segment parts in the region of an axially parallel radial chip-guide surface at different radial spacings from the drill axis with mutually partially overlapping working regions. At a transition point, the chip-guide surfaces merge into the flanks of the adjacent chip-conveying grooves. Disposed at at least one of the transition points is a transition surface which is gradually recessed so that it widens the cross-section of the chip space and merges into a flank of the adjacent chip-conveying groove.

FIELD OF THE INVENTION

The invention is related to a drilling tool for machine tools and amethod for the production thereof.

BACKGROUND OF THE INVENTION

A drilling tool of this type is known, which comprises a drill bodyhaving at least two chip transport grooves which are delimited at theirflanks by helical ribs and a cutting head which is disposed at the frontface side of the drill body. The cutting head has two segment portionswhich are radially outwardly delimited by partially cylindricalcircumferential surfaces and which are seperated from each other by chipspaces which end in the adjacent chip transport grooves in the directionof chip flow and which are aligned essentially parallel to the toolaxis. Further, the cutting head comprises at least two cutting insertswhich are each disposed in a recess of the segment portions in theregion of an essentially axially parallel radial chip breaker face,preferably with the face aligned to this, and which each have at leastone active cutting edge which protrudes axially over the cutting head,wherein the chip breaker faces each end in a helical flank of theadjacent chip transport groove at a transition point in the direction ofchip flow.

By a specific alignment of the cutting inserts which partially overlapin the active region of their cutting edges it is ensured that thelateral forces present at the cutting edges during drilling areessentially compensated by each other, so that a bore may be made in aworkpiece essentially without guidance. The chip spaces, which extendaxially parallel in the cutting head and which have a triangular crosssection, merge in the direction of chip flow into a comparatively steephelical chip transport groove, which is also of triangular crosssection. The chip transport grooves are delimited at their edges by ribswhich on the one hand serve to guide the drill within the bore and onthe other hand serve to delimit the chip transport grooves. The chipsare mainly forced out through the chip transport grooves under theaction of a coolant and lubricant which is supplied through the drillbody. By the design of the ribs to be relatively broad it is attemptedto prevent that the chips exit the chip transport grooves and distributethemselves over the circumference of the drill body, since this couldcause the chips to be fused to the bore wall and the drill body,damaging the bore and the drilling tool. A further problem consists inthat the chip space forms in the region of the cutting inserts, whichare displaced radially inwards with respect to the circumference, a chipspace of triangular cross section which tapers in the direction of chipflow in a funnel-like fashion. This leads to the circumstance that thechips may be formed to be relatively broad upon their creation and thenhave to be forced into the chip transport groove necessitatingdeformation work. By this a large part of the thrust imparted to thechips during the cutting process is lost in deformation work.Furthermore, the deformation forces are partially converted intotransverse forces, which causes a radial deflection of the drilling tooland therefore a degradation of the drilling efficiency and bore quality.

Based on this it is an object of the invention to develop a drillingtool which ensures an efficient and nearly lateral force-free chip flow,and which therefore may be used to create comparatively deep bores. Afurther object of the invention is to develop a method for theproduction of the drilling tool according to the invention.

SUMMARY OF THE INVENTION

The solution according to the invention is based foremost on therecognition that a chip deformation, which leads to a chip compressionand lateral forces, must be avoided in the region of the chip spaces andthe following chip transport grooves. In order to achieve this goal, thefollowing features are proposed according to the invention:

A drill body,

having at least two chip transport grooves which are delimited at theirflanks by helical ribs,

and comprising a cutting head which is disposed at the front face sideof the drill body,

which cutting head has at least two segment portions which are radiallyoutwardly delimited by partially cylindrical circumferential surfacesand which are seperated from each other by chip spaces which end in theadjacent chip transport grooves in the direction of chip flow and whichare aligned essentially parallel to the tool axis

and at least two cutting inserts which are each disposed in a recess ofthe segment portions in the region of an essentially axially parallelradial chip breaker face, preferably with the face aligned to this, andwhich each have at least one active cutting edge which protrudes axiallyover the cutting head,

wherein the chip breaker faces each end in a helical flank of theadjacent chip transport groove at a transition point in the direction ofchip flow,

wherein a transition face is located at at least one of the transitionpoints, which transition face recedes step-like from a limiting edge ofthe chip breaker face while broadening the cross section of the chipspace and which ends in a flank of the adjacent chip transport groove,

wherein the chip spaces have a chip guide face disposed at the adjacentsegment portion, which is positioned opposite the chip breaker face atthe side of the cutting insert and which, in a cross section through thechip space, includes an angle of 0° to 110° with the chip breaker face,

which chip guide face has a transition face at at least one of thetransition points, which transition face recedes step-like in the chipflow direction from a limiting edge of the chip guide face whilebroadening the cross section of the chip space and which ends in oneflank of the adjacent chip transport groove,

which limiting edge extends into the region between the active cuttingedge and the middle of the adjacent cutting insert, so that the crosssectional surface of the chip space continually increases from the tipof the cutting head to the chip transport groove,

wherein the drill body has a drill shank at its end opposite the cuttinghead, which shank is free of ribs and has a central coolant supply duct,

wherein coolant ducts are located in the ribs of the drill body, whichcoolant ducts are helically curved with the same curvature as the ribsand extend from the cutting head over the entire length of the ribs witha constant slant angle β with respect to the tool axis and end in thecentral supply duct in the region of the ribless drill shank,

and wherein the helix pitch of the chip transport grooves and therewithalso the width of the chip transport grooves increases continuously orstep-like in the chip flow direction.

The transition faces in the region of the chip breaker faces and thechip guide faces ensure that a thrust force which aids the chip removalis imparted to the chips created in the chip space upon their transitioninto the chip transport groove, without causing a chip deformation orchip compression.

In a drilling tool which is formed to be a stepped drill the drill bodycomprises at least two staggered portions which are axially seperatedfrom one another by a cutting crown and which have a step-likeincreasing diameter in the direction of chip flow. The cutting crowncomprises two segment portions which are delimited radially outwardly bypartially cylindrical circumferential surfaces and comprises at leastone cutting insert which is disposed in a recess of one of the segmentportions in the region of an essentially axially parallel radial chipbreaker face, preferably with its face aligned with respect to this, andwhich has at least one active cutting edge axially protruding over thecutting crown, wherein the corresponding chip breaker face ends at atransition point in the direction of chip flow in a helically curvedflank of the adjacent chip transport groove, and wherein a transitionsurface is located at the transition point, which transition surfacerecedes step-like in the direction of chip flow from a limiting edge ofthe chip breaker face while broadening the cross section of the chipspace and ends in one flank of the adjacent chip transport groove.

The stepped transition faces expediently extend over the entire width ofthe chip breaker face and/or of the chip guide face and are curvedconcavely in the direction of chip flow, so that they merge smoothlyinto the corresponding flank of the chip transport groove.

In order to improve the chip flow it is proposed according to analternative or preferred embodiment of the invention that at least inthe flank of the chip transport grooves at the cutting insert side aplurality of step surfaces or wave surfaces which recede from a steppededge or wavy edge extending radially or slanted with respect to the toolaxis in the direction of chip flow with a local broadening of the crosssection of the chip transport groove are disposed at an axial distancefrom each other. In this, the individual step surfaces or wave surfacesare delimited at their chip flow sided end by a further stepped edge orwavy edge extending radially or slanted with respect to the tool axis,wherein the individual step surfaces or wave surfaces have in thedirection of chip flow a gradient which initially increases and thendecreases with respect to the helix pitch of the corresponding grooveflank. The step surfaces or wave surfaces may be formed by depressionsin the flanks of the chip transport grooves on the cutting insert side,which depressions are either closed at their stepped edges or wavy edgesor open-edged in a radially outwardly direction. The depressions mayhave essentially any contour at their stepped edges or wavy edges,preferably an oval, circular or rectangular contour. The stepped or wavyedges ensure that a thrust force which aids the chip flow is imparted tothe chips within the chip transport grooves, without the occurrence ofchip deformation or compression.

In order to prevent the chips from exiting the chip transport grooves tothe circumferential region of the ribs, it is proposed according to analternative or preferred embodiment of the invention the flanks of thechip transport grooves have an included angle, as seen in cross sectionnear their outer edges, of less than 90°, preferably of 0° to 30°. Tothis end it is of advantage when the chip transport grooves have acontour which is partially circular in cross section, preferablysemicircular, wherein the cross section contour of the chip transportgrooves extends in a straight line toward their outer edge at least inthe region of one flank.

In order to improve chip flow, the chip space should be kept relativelyshort in the region of the cutting inserts up to the transition point.It is therefore expedient when the preferably curved limiting edge hasalong the length of its edge a variable distance from the edge of thecutting insert recess, which corresponds to 0.1 to 0.4 times thediameter of the limiting circle of the cutting insert. The partiallycylindrical circumferential surfaces of the segment portions and thepartially cylindrical circumferential surfaces of the ribs adjoining inthe chip flow direction expediently supplement each other to form acommon circumferential cylinder interrupted by the chip spaces and bythe chip transport grooves.

In order to ensure that the chips also cannot be deflected out of thechip spaces through the gaps remaining between the overlapping cuttingedges to the circumferential surface of the drill, a chip breaker facesection is proposed according to a preferred or alternative solution ofthe invention, which extends at the face side past a cutting edgeportion which lies within the mutually overlapping active portions. Thisproblem occurs mainly in the chip space which belongs to a cuttinginsert which is displaced radially inwards, so that the chip breakerface section should extend past a radially outward positioned cuttingedge portion of the radially innermost cutting insert. Generally it isalso possible that the chip breaker face section extends at the faceside past a radially inward positioned cutting edge portion of aradially outermost cutting insert, in order to bridge a gap locatedthere.

According to a further preferred or alternative solution of theinvention there is provided a chip breaker face limit which adjoins thepartially cylindrical circumferential surface of a segment portion andextends from the cutting head tip or cutting crown tip in the directionof the transition point and which extends in the direction of the chipspace past the plane of the face of a cutting insert which is displacedradially inwards with respect to the circumference. This effectivelyprevents that the chips created at the cutting edge are deflected towardthe partial-cylindrical circumferential surface. The chip breaker facelimit may protrude step-like or wedge-shaped over the plane of the facein a radial section. Additionally, the chip breaker face limit mayprotrude step-like or wedge-shaped over the plane of the face in anaxial section and diverge in the direction of chip flow under broadeningof the chip space, so that chip flow to the adjacent chip transportgroove is made easier.

In order to be able to provide chip transport grooves in the drill bodywhich are as deep as possible and which have a large cross section forthe passage of chips, it is of advantage when in a drill body having aribless drill shank which has a central coolant supply duct the coolantducts leading to the cutting head or crown are arranged within the ribssuch that they are helically curved with the same curvature as the ribsand extend from the cutting head over the entire length of the ribs witha constant slant angle with respect to the tool axis and end in thecentral supply duct in the region of the ribless drill shank. In orderto make their production easier, the coolant ducts form straightdeep-hole bores which extend slanted with respect to the tool axis in adeconvoluted state of the ribs. The slant angle of the deep-hole boreswith respect to the drilling tool axis is 1° to 8°, depending on thediameter and length of the drill body. Advantageously the deep-holebores lie in an axial plane which extends through the tool axis in thedeconvoluted state of the ribs, wherein the axial planes containing thetwo deep-hole bores include an angle different from 180° about the toolaxis. The angle included by the axial planes expediently is 155° to175°. With these measures a constant cross section change and thereforean increased rigidity and improved vibration damping is achieved. Themass distribution over the cross section can also be influenced by theangle included between the axial planes. Due to the design andarrangement of the coolant ducts according to the invention deep chiptransport grooves can be provided along the total length of the chipflow portion. The coolant ducts are arranged in a manner which isbeneficial with respect to flow properties. The slanted alignment withrespect to the drill axis results in a centrifugal force supported flowin the direction of the exit point.

A method for producing the drill tool according to the inventioncomprises the following steps:

a raw material body is machined to the drill tool shape, thereby forminga rotationally symmetrical, in sections cylindrical blank body which mayhave a plurality of stepped portions having different diameters;

two opposing chip transport grooves are formed or milled into acylindrical section (chip flow portion) of the blank body which areaxially delimited to both sides by a runout end, which chip transportgrooves are delimited at their flanks by remaining longitudinal ribs;

at the end of the blank body at the cutting head or cutting crown sidetwo chip spaces are formed or milled, which are delimited at theirflanks by an essentially axially parallel chip breaker face and a chipguide face, the chip breaker face and/or chip guide face of which cutacross the flanks of the adjacent chip transport groove in the region ofthe runout end at the cutting head or cutting crown side or within thecutting head, thereby forming a limiting edge and a step-like recedingtransition surface;

the chip transport grooves are formed or milled into the blank body orits stepped portions initially in the form of axially parallellongitudinal grooves;

before or after the forming or milling process deep-hole bores aremachined into the region of the straight ribs,

which extend slanted with respect to the cylinder axis of the blank bodyfrom points which are positioned eccentrically on the face of thecutting head or cutting crown side of the blank end in the direction ofa central blind bore in the ribless drill shank and penetrate itsbottom;

the blank prepared in this manner is clamped at bearing points which areaxially spaced with respect to each other and heated to a predeterminedtemperature in a ribbed zone which is located between the bearing pointsand subjected to a coaxial torsion moment and thereby helically twistedby a predetermined angle in the heated zone;

wherein the twisting angle is varied in the region of the ribs, formingan axially continuous or step-like increasing helical pitch.

In this, the chip transport grooves can be machined into the blank bodyby means of a side milling cutter and/or a cherry, wherein initially aconcave transition surface corresponding to the toroidal shape of theside milling cutter and/or the spherical shape of the cherry is createdat the runout ends at the cutting head or cutting crown side. This waychip grooves having a partial-circular cross section or a differentcontour can be milled, which have a straight runout toward the grooveedge at least at the groove flank at the cutting insert side. In orderto increase the rigidity of the drill body especially in the vicinity ofits clamping location at the drill shank, it is proposed according to apreferred embodiment of the invention that the longitudinal grooves aremilled into the cylindrical blank body with a depth which decreases inthe direction of chip flow. In order to be able to mill deep groovesextending up to the vicinity of the drill axis, it is of advantage whenthe chip transport grooves are initially milled into the blank body inthe form of axially parallel longitudinal grooves and when deep-holebores are made in the region of the straight ribs before or after themilling operation, which bores extend slanted with respect to thecylinder axis of the blank body from locations which are eccentricallypositioned on the face of the blank body end on the cutting head orcrown side in the direction of a central blind bore in the ribless drillshank, penetrating the bottom thereof. The blank prepared in this mannermay be heated to a predetermined temperature at a ribbed zone locatedbetween two axially spaced bearing locations and be subjected to acoaxial torsion force, thereby helically twisting the heated zone by apredetermined angle.

According to a preferred embodiment of the invention the blank the blankbody is twisted with a continuously or step-wise displaced heating zonein the region between the bearing points. In this way the twist anglemay be varied under formation of an axially variable helix pitch.

A further preferred embodiment of the invention provides that stepsurfaces or wave surfaces which are spaced at an axial distance fromeach other and are delimited by essentially radially extending edges aremilled at least into the groove flanks at the cutting insert side,preferably by means of a cherry. It is then of advantage when this isperformed before the helical twisting of the blank body.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is further described with reference tothe drawing, in which:

FIG. 1 shows a side view of a drilling tool with indexable cuttinginserts and helical coolant ducts;

FIG. 2a to 2d show four enlarged side views, rotated through 90° withrespect to each other, of the cutting head;

FIG. 2e shows a section along the line E--E in FIG. 2b;

FIG. 3 shows a front view of the cutting head;

FIG. 4 shows a section along the line IV--IV of FIG. 3;

FIG. 5 shows a longitudinal section through a blank for a drilling toolaccording to FIG. 1 to 4;

FIG. 6a to 6h show a process scheme for the production of the drillingtool;

FIG. 7a to 7c show two side views and a sectional view of a drillingtool having helical chip transport grooves which are wavy in thedirection of chip flow;

FIG. 8a to 8c show a stepped drill in a representation corresponding toFIG. 7a to 7c;

FIG. 9a and b show a detail of the flanks of the chip transport grooveson the cutting insert side, with stepped faces and wavy faces in anenlarged representation cut in the direction of chip flow;

FIG. 10a to 10h show details of the chip transport groove withdifferently designed contours of the stepped or wavy faces.

DETAILED DESCRIPTION

The drilling tool essentially consists of a drill shank 12 which isadapted to be clamped in a tool holder (not shown) and which has acollar 10 acting as a stop for the tool holder, and a drill body 14which comprises a cutting head 22 on its face side, which cutting headis provided with recesses 16 for a radially inner indexable cuttinginsert 18 and a radially outer indexable cutting insert 20, and ahelical chip removal portion 24 which extends from the cutting head 22to the collar 10. The chip removal portion has two oppositely arrangedchip transport grooves 26 which are delimited at their flanks by twohelically twisted ribs 28. Further, two coolant ducts 30, 32 arearranged in the chip removal portion 24, which ducts are helicallytwisted with the same pitch as the ribs 28, extend along the ribs overthe whole helical chip removal portion 24 with a constant slant angle βwith respect to the drill axis 34, and end in a common axially centeredsupply duct 36 in the drill shank 12 in the region of the collar 10. Thecentral supply duct 36 extends within the drill shank 12 up to theregion of the thickened collar 10. Its flow cross section is at leasttwice as large as that of the coolant ducts 30, 32. As can be seenespecially from FIG. 5, the coolant ducts 30, 32 open into the supplyduct 36 at radially offset transition points 37. In the blank state ofthe ribs 28 (FIG. 5)the axes 38, 40 of the deep-hole bores which formthe coolant ducts each lie in an axial plane which cutting through thebore axis or blank axis 34, respectively, which axial planes include anangle α≠180° about the drill axis 34 (cf. FIG. 4).

The cutting head 22, which is integrally connected to the drill body 14in the embodiment shown, comprises two segment portions 62 which areseparated from one another in a circumferential direction by axiallyaligned chip spaces 60', 60", which segment portions are radiallyoutwardly delimited by partial-cylindrical circumferential surfaces 64.The indexable cutting inserts 18, 20 are disposed in the region of theaxially parallel, radial chip breaker faces 66', 66" of the chip spaces60', 60", the faces 68', 68" of which cutting inserts are aligned withthe corresponding chip breaker face 66', 66" and the active cuttingedges 70', 70" of which protrude over the front face of the drill head22. The cutting edge 70" of the outer cutting insert 20 radiallyprotrudes by a small amount over the circumferential surface 64 of thecorresponding segment portion 62 and determines the bore diameter.

The chip spaces 60', 60" of the drill head 22 additionally comprise achip guide face 72', 72" disposed at the adjacent segment portion 62,which is located opposite the chip breaker face 66', 66" on the cuttinginsert side.

The chip breaker faces 66', 66" end in the direction of chip flow 74 ina limiting edge 76 which is designed to be a flank edge, which is joinedby a step-like receding transition face 80 which merges into theadjacent flank 84 of the chip transport groove 26 with a concavecurvature under broadening of the chip space cross section.

A depression 79 is machined, for example by means of an end millingcutter, into each of the the chip guide faces 72', 72", which extends tothe vicinity of the front tip of the drill body 14 and which has at itsfront face limiting edge 78 a step-like receding transition face 82having a concave curvature, and which merges smoothly into the adjacentflanks 86 of the chip transport groove 26 in the direction of chip flow.The limiting edge 78 extends into the region between the active cuttingedge 70', 70" and the center of the adjacent cutting insert 18, 20, sothat the cross sectional area of the chip space 60', 60" increasesconstantly from the tip of the cutting head 22 to the chip transportgroove 26.

As can be seen especially from FIG. 2a, c, d, and 3, a chip breaker facesection 88 is provided in the region of the chip breaker face 66'belonging to the innermost cutting insert, which extends over theradially outermost cutting edge portion 90 of the inner cutting insert18, which portion 90 lies within the overlapping active regions of thecutting inserts 18, 20. By this it is prevented that chips are deflectedinto the region of the circumferential surface 64 through the gussetbetween the cutting edge portion 90 and the bore, which gusset is formedduring the drilling operation. Additionally a chip breaker face limit 92which extends from the cutting head tip to the vicinity of transitionpoint is provided in the region of the chip breaker face 66', whichprojects in a radial and axial section in a step-like or wedge-likemanner over the plane of the chip face 68' of the cutting insert 18 inthe direction of the chip space 60' (FIG. 2d and 3). As can be seen fromFIG. 2a, the inner edge 94 of the chip breaker face limit 92 extendsslanted outwards in the direction of chip flow under broadening of thechip space 60'.

In the embodiments shown in FIG. 7 to 10 a plurality of stepped or wavysurfaces 104 which are disposed at an axial distance from each other areprovided in the flanks 84 of the chip transport grooves 26 on thecutting insert side, which surfaces are delimited by edges 106, 108which are aligned essentially radially (FIG. 7, 8, 10a, h) or slantedwith respect to the drill axis 34 (FIG. 10b, e, f, g). The stepped orwavy surfaces 104 jut back from the edges 106 at the cutting head sidein the direction of chip flow 120 under local broadening of the crosssection, and have an angle of ascent which initially increases and thendecreases in the direction of chip flow with respect to the helix pitchof the corresponding groove flank 84 (cf. FIG. 9a and b).

In the embodiments shown in FIG. 10a to h the stepped or wavy surfaces104 are formed by depressions in the flanks 84 of the chip transportgrooves 26 which are closed at their edges 106, 108 (FIG. 10b, c, d) oropen radially outwards (FIG. 10a, e to h). The depressions may forinstance have an oval (FIG. 10a, b, c), circular (FIG. 10d) orrectangular (FIG. 10e to h) outline at their stepped or wavy edges 106,108. They may be disposed spaced with respect to each other (FIG. 10c toh) or be adjacent to each other with their edges 106 and 108 (FIG. 10a)or they may overlap (FIG. 10b). In the embodiment shown in FIG. 8a to cthe drilling tool is designed to be a stepped drill. The drill body 14comprises three step portions 14', 14", 14'" which have diametersincreasing in steps in the direction of chip flow and which are axiallyseparated from each other by cutting crowns 110', 110". The cuttingcrowns 110', 110" comprise two segment portions 62' which are radiallyoutwardly delimited by partial-cylindrical circumferential surfaces 64',64" and which are separated from each other by chip spaces 60'" whichare aligned essentially parallel to the axis of the tool and which mergeinto the neighboring chip transport grooves 26 in the tool feeddirection as well as in the direction of chip flow. The cutting crowns110', 110" further each comprise a cutting insert 20' having an activecutting edge 70'" which protrudes axially over the cutting crown 110',110" and which is disposed in a recess of a segment portion in theregion of an essentially axially parallel chip breaker face 66'" withits face 68'" aligned thereto. The chip breaker face 66'" merges at atransition point in the direction of chip flow into a helically curvedflank of the adjacent chip transport groove 26. A transition face 80which recedes step-like from a limiting edge 76' of the chip breakerface 66'" in the direction of chip flow under broadening of the crosssection of the chip space and which merges into the one flank 84 of theadjacent chip transport groove 26 is located at the transition point.

As can be seen from the scheme of FIG. 6, the production of the drillingtool entails the folowing steps:

The cylindrical blank body 42' is turned in a lathe to yield the drillcontour and provided with the conical transition to the collar 10. Withthe blank still in the lathe, the central bore which forms the supplyduct 36 is machined from the shank side up to the region of the collar10 (blank 42").

Then the blank 42" prepared in this manner is mounted in a millingstation, where the opposing chip grooves 26 are machined by means of aside milling cutter 96 and a cherry 98 (cf. FIG. 1), leaving thelongitudianl ribs 28. The chip grooves 26 are machined to have a profilewhich is circular in cross section with spherical or toroidal runoutends 100, 102. In the milling station the clamping surface 98 is alsomachined into the drill shank (blank 42'"). In the instance of theembodiment of FIG. 7 and 8, the stepped or wavy surfaces 104 may also bemachined into the flanks of the chip grooves 26 on the cutting insertside by means of a side milling cutter.

The blank 42'" prepared in this manner is provided, in the same clampingor in a separate drill station, with deep-hole bores 30, 32 whichpenetrate the longitudinal ribs 28 from the front side exit points 50,52 in the drill head 22 to the supply duct 36 (blank^(IV)).

The blank 42^(IV) prepared in this manner is clamped at both ends 104,106 in a twisting station and heated in zones by means of an inductioncoil which is moved along the chip removal portion 24 of the drill body14, and is subjected to a coaxial torsional moment by way of theclamping points. By this the chip removal portion 24 together with thebores 30, 32 is successively helically twisted, wherein the helix anglemay be varied during the twisting process. By means of a cooling blowerwhich is disposed behind the induction coil it is ensured that thepreviously twisted portions of the chip removal portion are hardenedduring the subsequent twisting process (blank 42^(V)).

In order to compensate the form errors created during the twistingprocess the blank 42^(V) is once again machined in a lathe to form theblank 42^(VI).

In a final machining station the chip breaker faces 66', 66", the chipguide faces 72', 72", and the insert seats 16 are milled (blank42^(VII)). Lastly the head shape is milled, thereby forming the finisheddrill body 14.

In summary the following is to be stated: The invention is related to adrilling tool for machine tools. The drilling tool comprises a drillbody 14 having two chip transport grooves 26 which are delimited attheir flanks by helical ribs 28. A cutting head 22 is disposed at thefront face side of the drill body 14, which cutting head has two segmentportions 62 which are seperated from each other by two opposing, axiallyaligned chip spaces 60', 60", and two cutting inserts 18, 20 which areeach disposed in a recess 16 of the segment portions in the region of anaxially parallel radial chip breaker face 66', 66" at different radialdistances from the drill axis 34 with partially overlapping activeregions. The chip breaker faces 66', 66" end in the flanks 84 of theadjacent chip transport grooves 26 at a transition point, wherein atransition surface 80 which merges into a flank of the adjacent chiptransport groove 26 and which recedes step-like under broadening of thecross section of the chip space 66', 66" is diposed at at least one ofthe transition points.

We claim:
 1. A drill tool for machine tools comprising a drill bodyhaving at least two chip transport grooves which are delimited at theirflanks by helical ribs,and comprising a cutting head which is disposedat a front face side of the drill body, the cutting head having at leasttwo segment portions which are radially outwardly delimited by partiallycylindrical circumferential surfaces and which are separated from eachother by chip spaces which end in the adjacent chip transport grooves ina direction of chip flow and which are aligned essentially parallel to atool axis, and at least two cutting inserts which are each disposed in acutting insert recess of the segment portions in a region of respectiveessentially axially parallel radial chip breaker faces and the cuttinginserts each having at least one active cutting edge which protrudesaxially over the cutting head, wherein the chip breaker faces each endin a helical flank of the adjacent chip transport groove at a transitionpoint in the direction of chip flow, wherein a first transition face islocated at at least one of the transition points, which transition facerecedes step-like from a first limiting edge of the chip breaker facewhile broadening a cross section of the chip space and which ends in aflank of the adjacent chip transport groove, wherein the chip spaceseach have a chip guide face disposed at the adjacent segment portion,which is positioned opposite the respective chip breaker face at theside of the cutting insert and which, in a cross section through thechip space, includes an angle of 0° to 110° with the chip breaker face,the chip guide face having a second transition face at at least one ofthe transition points, the second transition face receding step-like inthe chip flow direction from a second limiting edge of the chip guideface while broadening the cross section of the chip space and ending ina second flank of the adjacent chip transport groove, the secondlimiting edge extending into the region between the active cutting edgeand the middle of the adjacent cutting insert, so that the crosssectional surface of the chip space continually increases from the tipof the cutting head to the chip transport groove, wherein the drill bodyhas a drill shank at its end opposite the cutting head, said shank freeof ribs and having a central coolant supply duct, wherein second andthird coolant ducts are located in the ribs of the drill body, saidsecond and third coolant ducts are helically curved with the samecurvature as the ribs and extend from the cutting head over the entirelength of the ribs with a constant slant angle (β) with respect to thetool axis, and end in the central supply duct in the region of theribless drill shank, and wherein the helix pitch of the chip transportgrooves and the width of the chip transport grooves increasecontinuously or step-like in the chip flow direction.
 2. The drill toolof claim 1, wherein at least some of the cutting inserts are located atdifferent radial distances from the tool axis and have partiallyoverlapping active regions.
 3. The drill tool of claim 2, wherein thecutting edge of the at least one radially most outwardly positionedcutting insert radially protrudes over the corresponding partiallycylindrical circumferential surface.
 4. The drill tool of claim 1,wherein the drill body comprises at least two staggered portions whichare axially separated from one another by a cutting crown and which havea step-like increasing diameter in the direction of chip flow, thecutting crown comprising two cutting crown segment portions which aredelimited radially outwardly by partially cylindrical circumferentialcutting crown surfaces and comprising at least one cutting crown insertwhich is disposed in a recess of one of the cutting crown segmentportions in the region of an essentially axially parallel radial cuttingcrown chip breaker face and the cutting crown insert having at least oneactive cutting edge axially protruding over the cutting crown, whereinthe corresponding chip breaker face ends at a transition point in thedirection of chip flow in the flank of the adjacent chip transportgroove.
 5. The drill tool of claim 1, wherein the transition faces arecurved concavely.
 6. The drill tool of claim 1, wherein the transitionfaces merge smoothly into the respective flanks of the chip transportgrooves.
 7. The drill tool of claim 1, wherein the transition facesextend over the entire width of the respective chip breaker faces. 8.The drill tool of claim 1, wherein the flanks of the chip transportgrooves include in cross section near their outer edges an angle of lessthan 90°.
 9. The drill tool of claim 1, wherein the chip transportgrooves have a contour which is semicircular in cross section.
 10. Thedrill tool of claim 9, wherein the cross section contour of the chiptransport grooves extends in a straight line toward their outer edge atleast in the region of one of the flanks.
 11. The drill tool of claim 1,wherein the first limiting edge has along a length of its edge avariable distance from the edge of the cutting insert recess, whichcorresponds to 0.1 to 0.4 times the diameter of a limiting circle of thecutting insert.
 12. The drill tool of claim 1, wherein the partiallycylindrical circumferential surfaces of the segment portions and thepartially cylindrical circumferential surfaces of the ribs adjoining inthe chip flow direction supplement each other to form a commoncircumferential cylinder interrupted by the chip spaces and by the chiptransport grooves.
 13. The drill tool of claim 2, wherein a chip breakerface section extends past a cutting edge portion which lies within thepartially overlapping active portions.
 14. The drill tool of claim 2,wherein the chip breaker face section extends past a radially outwardpositioned cutting edge portion of a radially innermost one of thecutting inserts.
 15. The drill tool of claim 13, wherein the chipbreaker face section extends past a radially inward positioned cuttingedge portion of a radially outermost one of the cutting inserts.
 16. Thedrill tool of claim 1, wherein a chip breaker face limit which adjoinsthe partially cylindrical circumferential surface of one of the segmentportions extends from the cutting head tip in the direction of thetransition point and extends in the direction of one of the chip spacespast the plane of a face one of the cutting inserts which is displacedradially inwards with respect to the circumferential surface.
 17. Adrill tool for machine tools comprising a drill body having at least twochip transport grooves which are delimited at their flanks by helicalribs, and comprising a cutting head which is disposed at a front faceside of the drill body, the cutting head having at least two segmentportions which are radially outwardly delimited by partially cylindricalcircumferential surfaces and which are separated from each other by chipspaces which end in the adjacent chip transport grooves in a directionof chip flow and which are aligned essentially parallel to a tool axisand at least two cutting inserts which are each disposed in a cuttinginsert recess of the segment portions in a region of an essentiallyaxially parallel radial chip breaker face and the cutting inserts eachhaving at least one active cutting edge which protrudes axially over thecutting head, wherein the chip breaker faces each end in a helical flankof the adjacent chip transport groove at a transition point in thedirection of chip flow, wherein a chip breaker face limit which adjoinsthe partially cylindrical circumferential surface of a segment portionand extends from a tip of the cutting head in the direction of thetransition point and which extends in the direction of the chip spacepast the plane of a face of the cutting insert which is displacedradially inwards with respect to the circumferential surface.
 18. Thedrill tool of claim 17, wherein the chip breaker face limit protrudesstep-like or wedge-shaped over the plane of the face in a radial oraxial section.
 19. The drill tool of claim 17, wherein the chip breakerface limit diverges in the direction of chip flow while broadening thechip space.
 20. The drill tool of claim 1, wherein at least in the flankof the chip transport grooves at a cutting insert side, a plurality ofstep surfaces or wave surfaces recede from a stepped edge or wavy edgeextending radially or slanted with respect to the tool axis in thedirection of the chip flow.
 21. A drill tool for machine toolscomprising a drill body having at least two chip transport grooves whichare delimited at their flanks by helical ribs, and comprising a cuttinghead which is disposed at a front face side of the drill body, thecutting head having at least two segment portions which are radiallyoutwardly delimited by partially cylindrical circumferential surfacesand which are separated from each other by chip spaces which end in theadjacent chip transport grooves in a direction of chip flow and whichare aligned essentially parallel to a tool axis, and at least twocutting inserts which are each disposed in a recess of the segmentportions in a region of respective essentially axially parallel radialchip breaker faces and the cutting inserts each having at least oneactive cutting edge which protrudes axially over the cutting head,wherein the chip breaker faces each end in a helical flank of theadjacent chip transport groove at a transition point in the direction ofchip flow, wherein at least in the flank of the chip transport groovesat a cutting insert side, a plurality of step surfaces or wave surfacesrecede from a stepped edge or wavy edge extending radially or slantedwith respect to the tool axis in the direction of chip flow with a localbroadening of the cross section of the chip transport groove, whereinthe plurality of step surfaces or wave surfaces are disposed at an axialdistance from each other.
 22. The drill tool of claim 21, wherein theindividual step surfaces or wave surfaces are delimited at a chip flowsided end by a further stepped edge or wavy edge extending radially orslanted with respect to the tool axis, wherein the individual stepsurfaces or wave surfaces have, in the direction of chip travel, agradient which initially increases and then decreases with respect to ahelix pitch of the corresponding flank.
 23. The drill tool of claim 21,wherein the step surfaces or wave surfaces are formed by depressions inthe flanks of the chip transport grooves on a cutting insert side,wherein the depressions are either closed at the stepped edges or wavyedges or open-edged in a radially outwardly direction.
 24. The drilltool of claim 23, wherein the depressions have an oval or circularcontour at the stepped edges or wavy edges.
 25. The drill tool of claim23, wherein the depressions have an opened-edged rectangular contour attheir stepped edges or wavy edges.
 26. The drill tool of claim 21, thedrill body having at its end opposed to the cutting head a ribless drillshank which has a first central coolant supply duct, and second andthird coolant ducts are located in the ribs of the drill body, and arehelically curved with the same curvature as the ribs and extend from thecutting head over the entire length of the ribs with a constant slantangle (β) with respect to the tool axis and end in the central supplyduct in the region of the ribless drill shank.
 27. A drill tool formachine tools comprising a drill body, having at least two chiptransport grooves which are delimited at their flanks by helical ribs,and comprising a cutting head which is disposed at the front face sideof the drill body, the cutting head having at least two segment portionswhich are radially outwardly delimited by partially cylindricalcircumferential surfaces and which are separated from each other by chipspaces which end in the adjacent chip transport grooves in a directionof chip flow and which are aligned essentially parallel to a tool axis,and at least two cutting inserts which are each disposed in a recess ofthe segment portions in a region of respective essentially axiallyparallel radial chip breaker faces and the cutting inserts each havingat least one active cutting edge which protrudes axially over thecutting head, wherein the chip breaker faces each end in a helical flankof the adjacent chip transport groove at a transition point in thedirection of chip flow, wherein the drill body has at its end opposed tothe cutting head, a ribless drill shank which has a central coolantsupply duct, and second and third coolant ducts are located in the ribsof the drill body, wherein the second and third coolant ducts arehelically curved with the same curvature as the ribs and extend from thecutting head over the entire length of the ribs with a constant slantangle (β) with respect to the tool axis, so that they directly end inthe central supply duct in the region of the ribless drill shank. 28.The drill tool of claim 27, wherein the second and third coolant ductsform straight deep-hole bores which extend slanted with respect to thetool axis in a deconvoluted state of the ribs.
 29. The drill tool ofclaim 28, wherein the deep-hole bores lie in an axial plane whichextends through the tool axis, wherein the axial planes containing thetwo deep-hole bores include an angle (α) different from 180° about thetool axis.
 30. The drill tool of claim 29, wherein the angle (α)included by the axial planes is 155° to 175°.